Party-line telephone system



H. G. DuilAMEL Erm.

PARTY LINE TELEPHONE SYSTEM Match 3l, 1953 10 Sheets-Sheet l Filed April 5, 1948 mz3 Oom March 31, 1953 H. G. DUHAMEL Erm. 2,633,496

l PARTY LINE TELEPHONE SYSTEM Filed April 5. 1948 16 sheets-sheet 2 E00 FIG.- 2.

FIG. 3.

FROM OTHER GROUPS TO OTHER GROUPS TWO WAY TRUNK` 7/0 T0 OENTRAL OFFICE F I G. 4. 7

f REGISTER l 7 LINK IN NT R5 HOWARDV DUOHAMEL RAYMOND A. REED BY EDWARD O. CAMPBELL REGISTER March 3l, 1953 H. G. DUHAMEL ETAL 2633,496

-PARTY LINE TELEPHONE SYSTEM Filed April 5, 1948 A' 1o sheets-sheet s M FlG. 3u. 700

INVENTO RS HOWARD G. DUHAMEL RAYMOND A. REED /BY EwD CAMPBELL 2 ATTORNE `'Maan-ch V31, 1953 H. G. DUI-'IAMEL l-:TAL 2,533,496

P ARTY L INE TELEPHONE SYSTEM Filed April 5. 1948 10 Sheets-Sheet 4- INVENTORS HOWARD (i` DUHAMEL RAYMOND A. REED BY EDWARD 0. CAMPBELL PARTY LINE TELEPHONE SYSTEM Filed April 5, 1948 10 Sheets-Sheet 5 F IG. 5c..

INVENTOR S Y 0. CAMPBELL March 31, 1953 H, G. DUHAMEL ETAL 2,633,496

PARTY LINE TELEPHONE SYSTEM Filed April 5, v1948 10 Sheets-Sheet 6 lNvEGN-rons L 4 nAmoNn 'A. REED BY EDWARD 0. CMPLL March 3l, 1953 H. s. DUH'AMEL Erm. 2,633,496

PARTY LINE TELEPHONE SYSTEM Filed April 5, 1948 10 Sheets-Sheet 7 INVENTORS HUWA 6. DLHAME RAYMOND A. REED FIG. 4b. ,W

March 31, 1953 H. G. DUHAMEL ETAL A 2,633,496

PARTY LINE TELEPHONE SYSTEM l Filed April 5, 1948 10 Sheets-Sheet 8 F l G 4 c I INVENTORS HOWARD G. DUHAMEL RAYMOND A. REED BY EDWARD 0. CAMPBELL March 3l, 1953 A' H. G. DUHAMEL ETAL 2,633,495

PARTY LINE TELEPHONE SYSTEM Filed April 5, 1948 10 Sheets-Sheet 9 INVENTO RS HOWARD G. DUHAMEL RAYMOND A REED gyn o, CAMPBELL ATTRNEY FIG. 4d.

March 31, 1953 H. G. DUHAMEL ET A1. 2,633,496

PARTY LINE TELEPHONE SYSTEM Filed April 5, 1948 10 Sheets-Sheet l0 l FIG. 5.`

FIG. 3a. |`|G 3b. HG 5cl sua LINES (6a.) (6b.) 4(6c.)

FIG. 4a. Fl G. 4b.

FIG. 4c; FIG. 4c. (7c) (7d.)

INVENTOR S HOWARD G. DUHAMEL RAYMOND A. REED Patented Mar. 31, 1953 f Y- UNITED STATES PATENT OFFICE PARTY-LINE TELEPHONE SYSTEM Application April 5, 1948, Serial No. 19,027

13 Claims. l

` This invention relates to new and useful means in a. community for establishing connections between subscribers in automatic switching systems and is more particularly related to the two-way trunk circuits and the trunk links by means of which such calls are established.

In small community automatic systems of the type to which this invention relates, the call number consists of four digits, the first three of which designate the line number which identifies the location of the line in the final selector terminal banks. The fourth digit designates the type of ringing current to be sent over the call line to ring one of the parties on a multi-party line.

According to one feature of the invention, the trunk circuit is arranged to repeat the dial pulses received from the central oflice operator to the register link and to the register. A rotary switch, called the trunk marker switch, in the trunk circuit is stepped coincidently by the impulses of the rst digit to determine if the number dialed represents an assigned hundreds digit or not.

According to another feature of the invention the trunk marker switch, after being stepped by the impulses of the first digit, is stepped to a definite predetermined position and advances only onestep for each of the tens and units digits.

Still another feature of the invention provides for the stepping of the trunk marker switch in accordance with the pulses of the fourth or ringing digit thus advancing the wipers of the switch from the previous position, in which it was set as the result of the dialing of the first three digits. During this setting of the marker switch the pulses are not transmitted beyond the trunk circuit.

According to another feature of the invention, the ringing `current sent to the called line is determined by the position of the trunk marker switch from the trunk circuit and if the called line is busy, the trunk circuit receives a line busy signal and thereupon sends a flashing busy signal to the operator.

According to still another feature of the invention, the trunk may be seized by the selector of a trunk link when a subscriber makes a call to the operator and automatically signals the operator of the presence of such a call.

Thetrunk link provides the transmission circuit which supplies talking battery to the local subscriber and sends reverse battery supervision to the operator and the trunk link is arranged to connect the line conductors of the local subscriber directly to the transmission circuit of the trunk.

The above mentioned and other features and objects of this invention and the manner of obtaining them will become more apparent and the invention will be best understood by reference toy the following description of an embodiment of,

the invention taken in conjunction with the accompanying drawings which show the two-way trunk link circuits in detail and the related switching apparatus in block diagram form, wherein:

Fig. 1 shows in diagrammatic form the switches' Fig. 3 shows thev trunk link circuit when Figs..V

3a, 3b and 3c are placed together in accordance with Fig. 5.

Fig. 4 shows the two-Way trunk circuit when.

Figs. 4a, 4b, 4c and 4d are placed together as shown in Fig. 5.

Fig. 5 shows the relation of the portions of the various figures and how they should be put t0- gether to form the circuits.

General description Fig. 1 illustrates diagrammatically a system The well known 10D-pointr serving 200 lines. power driven switch having seven brushes is employed as a register link line iinder |06, a linev nder I l0 and a iinal selector ||2. A register link circuit |01 employs, in addition to the line nder |06, a rotary step-by-step switch |08 to'select an idle register |09. Each local link circuit has a line nder ||0 and the nal selector ||2. All seven brushes are used on the line nder but only four of the brushes in the final selector are used for calls within the line group served by the associated local link. On calls to other hundred line groups the other three brushes and one of the rst four mentioned of the final selectorV are employed.. Access to the local link |I| may be had from the other local links |22 over a three.- wire circuit |28.

, Trunk lines IM and |25 are employed which. are similar to the local links and |22 except. that they contain metallic transmission circuits. without battery supply, whereas the local links and |22 supply battery through a condenser feed bridge.

Two-way interofce trunk circuits |21 are em.

ployed which terminate in a six Kconductor circuit, three of which are used for the line circuit,

at nal selectors of the trunk link circuits |4` and |25 while the other three serve for hunting the line finders I 06, I I and I i3, the iinal selectors ||2 and |I5, links |01, III and H4, register selectors |08, registers |09 and two-way trunks |21 need be provided in suicient quantities to satisfy trafiic requirements. An installation for 200 lines does not require duplication of all equipment but the lines of group |03 need their own line nders IIS, |2I and |24 and final selectors |23 and |20, with appropriate local and trunk links |22 and |25 and register links I|9,.which may be con nected with registers |09 via register selectors |20. It will be understood, of course, that while 200 lines are referred to in this embodiment by way of example only, many more 100 line groups are contemplated.

The two-way trunk circuits like |21 are accessible to all the groups over the multiple |3I. These trunk circuits |21 terminate in conductors |30 on the banks of the line iinders |00 and II3. They require line numbers but no line circuits. The line numbers of the trunk circuits need not be consecutive.

When the subscriber |02 belonging to the 200 line group calls, the line relay energizes the start circuit, not shown, which starts the line finders |00 of all the idle register links |01 serving the 200 group of lines and places potential on the test terminals of the register link line finders |00. The line finders |00 of the register links 10i hunt together and when one nds the calling line, the line cutoff relay is energized andthe energizing condition is withdrawn from the start circuit which removes the test potential from the test terminals. As soon as the line finder |00 of a register link iinds the line, an idle register |09 is selected by the register selector |08 and when the register is attached to the link |01, dial tone is transmitted from the link to the calling line |02.

The subscriber now dials the call number and dial pulses are repeated by a relay in the register link |01 not only to the register circuit |09 but to a rotary switch, called the link marker switch, in the link |01. Impulses of the first digitposition the link marker switch. The first digit dialed is the hundreds digit of the local line number or the single code digit for a trunk.

If the hundreds digit designates the same group of 100 lines, in which the calling line is located, three relays are operated that adjust the link |01 to signal the register |00 that final selection is not to be made in accordance with the hundreds digit and the final selector |I2 of the local link is selectively operated to connect called with the calling line.

If the hundreds digit designates some other group, e. g. 300 line group, two of the three relays are operated and the register is signaled to selectively operate the iinal selector II2 as a group selector to select the group of trunks in accordance with the hundreds digit and to hunt for an idle trunk |28 leading to a nal selector in the desired 100 line group. The selected nal selector in this example would be one like |23 and it is then operatedk to select line |03 in the 300 line group.

If the hundreds digit designates an unequipped group, the register link |01 releases and the line is locked out.

If the code is dialed, another relay is operated which adjusts the register link |01 to start line finder I I3oi a trunk link I I4 and to use the nal selector |I to hunt for an idle two-way trunk circuit |21.

All of the selectors are controlled by the registeron a local call. The tens and units digits are not registered in the register link |01 but the above mentioned link marker switch in the link is arranged to move to position 9 after the first digit is dialed and the above operations take place provided that digit signifies a local line. Provision is made for release when the digit designates an unequipped line group. Thus positions 10 and 11 of the link marker switch absorb the tens and units digits.

After the first digit has been dialed, the line iinders IIO of the idle local links III or I|3 of a trunk iink H4, designated by the dialing of the iii-st digit as above described, are started and one of them seizes the calling line.

A fourth digit is dialed by the calling subscriber to select the called station in a ten party ringing system. This moves the link marker switch in the register link |01 to a position for connecting the proper ringing current to the link for ringing the bell of the desired party.

When the called subscriber answers, the register link |01 is disconnected and the local link supplies battery for conversation. If the called subscribers line is busy, busy tone is supplied from the register link |01. The called line is tested by the register |09 which signals the register link that the called line is busy or idle.

On an inward call the two-way trunk |21 obtains the register link |01 and the dial pulses are recorded as above described. On Such calls a trunk link I Irl is used on account of the transmission battery supply but the operation is substantially the same as above.

Detailed description The attached drawings show the circuit for establishing the connections described above in general terms with reference only to central ofce calls which involve the trunk link and two-way trunks that form the subject mattei of this application. The connections to the ringing generator and the various tone and interrupters are marked to indicate the purpose of such conductors.

In Fig. 2 is shown a subscribers line circuit 200, a trunk link H, a register link |01 and a register circuit |00 in block form with the connecting conductors and in suiiicient detail to show how these circuits operate in conjunction with the trunk link of Fig. 3 and the two-Way trunk circuit of Fig. 4.

The drawings show the contacts of a given relay related by a iine line to the relay winding which controls them. The description is divided into sections as follows:

A-Local subscriber calls the operatorl. Attaching a trunk link 2. Trunk selection 3. Operation of two-way trunk circuit 4. Release B-Incoming call from a manual operatorl. Register link attached 2. Reception of the rst, second and third digits Attaching a trunk link Selection of a called line in same hundreds group Test of called line Called line tests free Called line tests busy Reception of fourth digit and ringing Selection of a called line in a different hundreds group l0. Talking, supervision and release AVV-LOACAL sUBscRiBER VCALLS THE'OPER ATOR The subscriber at station 206 lifts his receiver and dials 0 to make a call to the operator. This causes the line iinder |66 of the register link |61 to attach the register link to the calling line and register selector |06 selects an idle register |69. A relay is operated in the register link as the result of the ten dial pulses received, which adjusts the register link and the register to start the line iinders ||3 of the idle trunk,

links I I4.

1.-Attaching a trunk Zink The operation of av relay in the register link circuit energizes the start circuit which connects test potential from battery, resistance 843, conductor 36|, brush 365 of the link line nder to conductor v2 I6 as shown in Fig. 2. The start circuit also connects ground to conductor 626 for operating the line finder lclutch magnet of all free trunk links.

Referring to Fig. 3, the brushes vof the line finders rotate until brush 606 of one of them encounters test potential 0n conductor 2|3 to operate relay 663. Relay 666 releases clutch niagnet 661 to stop the line finder and connects ground through a low resistance path consisting of the winding of relay 669 in series with the second winding of relay 668 to brush 666. Relay 609 is operated and this low resistance path shunts down the test potential making the circuit busy. lf a double test should occur, i. e. two line nders test the same line at the same time, there is insufficient current to holdboth relays 608 or to operate relay 666. The rst relay 668 to release removes its low resistance shunt allowing the other relay 668 to hold. The former circuit remains normal and waits for the next call. Relay 666 operates relay 62| and closes a circuit from nder brush 661i to relay 646 to permit the reception of the group selection signal.

Relay 62| locks to ground in the register link circuit via link line finder brush 366, conductor 2I6, and trunk line finder brush 665. The operation of relay 62| opens the circuit from incoming conductor 625 to relay 626 to prevent selection of the link by a group selector and operates relay 622. The registery link circuit releases the start circuit which opens ground from conductor 629 to stop all free line finders and removes test potential from conductor 36|. Relay 622 opens the circuit of relays 66S and 669, and prepares the circuit from nder brush 666 to selector brush SI5, opens the circuit for clutch magnet 661 to prevent the line nder from moving on the release of the test relays, opens the restoring circuit to clutch magnet 651 oi the selector and provides a general operating and locking ground for the trunklink circuit.

2.-Trunk selection The trunks to the operator are connected in multiple to the trunk link selectors of all hundreds groups as shown in Fig. 1. Before the test relay 666 can release a momentary ground is connected to -brush 364 of the link line finder, conductor `EIS, brush 664 of the trunk link line finder, a front contact of relay 606 to operate relay 648. Relay 648 locks to ground at a contact of relay 622 and transfers the link conductors from selector brushes 6H] and 6| I to brushes `6| 3 and 6M, respectively, via contacts of relay 645 to utilize the terminals inthe lower half of'the selector arc and operates'rel'ay 641 whichl connects selector brush 6I5 to finder brush 606 and opens the circuit to selector brush SI2.

Ground from a relay of the register, is connected via conductor 31|, wiper 323 of the regis ter selector, the register link circuit, brush 303 of the link line nder, conductor 2|1, brush 66,3y

of the trunk line nnder, front contact of relay 62|, back contacts of relays 631 and 636, and offnormal contact 630, to operate relay 6I8. The ground is extended through the winding of selector clutch magnet 6I1 to battery to operate the clutch magnet. The selector brushes rotate and revertive pulses from selector brush 6|6 operate relay 429 of the register via back contacts;

of relays 633, 636 and 631, front contact of relay 62|, trunk line iinder brush 664, conductor 2I8,: link line finder brush 304, the register link circuit, wiper 324 of the register selector, conductor 312, to relay 42S.

When the register has received the allottedv number of pulses the selector proceeds to hunt for an idle trunk under Vthe control of the regis. A relay 422 is connected through conductor.

nder to operate relays V6|8 and clutch magnet:

6I1. Selector brushes rotate in this circuit until relay 422 operates. A slow relay in the register measures the time during which the trunk test:

may take place. If no idle trunk is found when this relay operates selector brushes rotate to the rst trunk of the next group where ground via selector brush 6I6 of the previously described circuit operates relay 429 to stop the rotation of the switch. If all trunks are busy the register is released and busy tone is sent to the calling subscriber and the trunk link is released.

If the selected trunk is free, the register connects ground through a resistance 425 via con-v ductor 31|, wiper 323 of the register selector, the register link, link line finder brush 363, conductor 2I'i and trunk line iinder brush 663 to operate relay SIS but not clutch magnet 6I1. Relay SIS short circuits relay 634 and holds relay 633. Relay 634 releases and operatesrelay 636 via a contact of reay 633.Relay 636 locks to a contact of relay 622 and connects relay 635 via selector brush SI5, conductor 102, back contacts of relays 136, 'E35 and 1|5, jack 1.56, to relay 134 of the two-way trunk.

The free trunk signal from the register connectsbattery via resistance 344, brush 365 of the link line nder, conductor ZIB, brush 666 of the trunk line finder, front contacts of relays 622 and 636, windings of relays 64I and 642in series, to operate relay 642 but not relay 64I. Relay 642 operates relay 644 which locks to holding ground from relay 622. Relays 343 and 366 release the register links since the second holding path for relays 366 and 326 is opened, by relay 333. Relay 635 operates relay 631 which connects ground resistance 646 to hold cutoff relay 265 of the calling line Via back contact of relay 62|, trunk iinder brush 602 and conductor 2I5. Relay 664 locks to ground from relay 635, operates relay 6|9, opens the ground pathto relay 668 to prevent further testing by the trunk n nder and connects battery via resistances 61H)V and E42 to selectorbrush B13 and 'conductor '153 until relay `615 operates.

The release ofthe register Alink releases frelays 621 and 622. Relay 621 'completes the-holding path to cutoff relay 202 from-relay 631 and opens the paths to trunk finder Ylorushes 1503 and 555. The calling subscriberis now connected to 'the trunk and relay E35 VVconnects ground-.for y.holding rela'ys 536, i633, i 6113, 511B' and 6114.

3.-O.pe'ration.of :two-way trunk circuit Relay 134 4of the two-way trunk circuit operates rom'ground Via relay 635 oi-.thetrunk link, selector brush 615, conductor 162, contacts of relays 136, 135-and 115 andjack 150 and-opens the `path for relay 136 vand kprepares the circuits for relays 113, 1111 and 1311. The momentary battery signal from-the trunk link via conductor 11311 operates .relay 1.21 in advance of :the connection of the subscribers line conductors 213 and'214 through the trunk link by the operation of relay 619 to conductors 161) and 1111 and relay 121 .is then held by the calling subscriber. Relay 1.21 operates relays 112 and 113. Relay 'H2 reverses the battery and ground connections f to trunk conductors 116 and 111 to operate a signal, not shown, before an operator in .the distant exchange.

Relay 1111 is operated from battery, winding of relay 1111, Yfront contacts of relays 113 and 134 to ground 'on wiper 121 in normal position of the trunk marker switch. Relay 114 operates from `contacts of .relays 1111 and 16E and, in turn, operates relay 1.15. Relay 115 connects ringing tone from 'conductor 1158 via front contacts lof relays 115 and 112, `.loackcontact of relay 141, condenser 251, "and back contact of relay v133 to conductor 191. Relay 1311 operates from ground via front contacts of :relays 134, 11-5 and 112 and prepares a circuit for the pay station line signal.

The equipment in the distant :exchange is not shown but it is assumed that the line and supervisory signals are operated by reversing the current in the trunk Vconductors and that a calling dial may be connected to the trunk conductors i1 for controlling the sending of dial pulses.

When the operator answers by connecting to the line, relay 133 operates and transfers the operating ground for relay 11E to the holding ground for relay 113. Relay 114 releases and, in turn, releases relay 115 which disconnects the ringing tone, opens thecircuit of relay 133 and completes a path for the pay station tone .from conductor 1112 to .repeating coil 116 via back contacts of relays 136, 135 and 115, jack 158, a contact of relay 1311, back contact oi relay 115, front contact of relay 112, back contact of relay 141, condenser 151 and back contact of relay 135. Relay 136 is slow releasing to provide time for the signal to be sent. If the operator should miss the signal, it can be repeated by disconnecting momentarily, thus reoperating relay .136 which will reconnect the signal.

The connection is now complete over the repeating coil bridge 116, and condensers 118 and 119.

tf-Release 8. lay 108 releases to open the holding .path for relay 143 via conductor 102, selector brush 615 and relay 535 of the trunk link so that, when relay 161 releases, relay 635 canirelease. Relay 635 releases-'relays 631, 619, 636, S48-and 644. Relay 6d8 releases relay 641 and 'completes the restoring vpath for the selector lclutch magnet 611 which returns theiselector to normal over its I'own ofnormal 4contact 632 via contacts Alof relays y6111 4and `622. The trunk link and the two-way trunk'rcircuits .are now free for new calls.

B-INCOMING CALL FROM A MANUAL OPERATOR 1,-Reyster Zink attached It will be assumed fthat the tWo-way'trunks form a part `of line group Y201) and are connected via conductors 11111, '1111, 102, 1113, 105 and 106 to the multiple terminals ofthe line iinders of the register and ytrunk links. When the operator makes a call, a bridge, not shown, on trunk conductors 116 and 111 operates relay 10B. Ground from a contact of relay 108 operates relays 113 in an obvious -circuit and relay 136 via back contacts of relay 151 and 134. Relay 136 disables relay 134, prepares a circuit for-relay 135, connects ground to conductor 1133 to signal the register link, when attached, that the call is a trunk call, connects starting potential through resistances 162 and 143 to conductor 165 similar to those of a calling line and operates relay 112 which reverses the polarity over trunk conductors 116 and 111. This reversal indicates to the operator that the trunk is hunting a register link and register.

The starting potential on conductor 155 operates the starting circuit to complete the circuit for the register link line finder magnets of any free register link line finders and to connect ground to the test relays. When a register link line nder brush 3116 encounters test potential on conductor 1135, it stops the line nder and reduces the starting potential on conductor 154 and all the link line nnders stop. A free register is attached to the register link by the register selector.

Ground from a contact of relay 135, conductor 163, link line finder brush 3113 operates relay 335 to prepare the register link circuit for an incoming call. Relay 335 locks to the register link holding ground. Ground via resistance 355, link line finder brush 302, conductor 152 and a contact of relay 136 operates relay 135 which locks to conductor 102. Relay prepares a locking path for itself to a contact of relay 161 and. an operating path for relay 128 Via front contacts of relays 1111 and -135 and back contact of relay 1413, prepares the dial impulse circuit, opens the circuit for relay 134, and operates relay 131 from ground on Wiper 121 in the normal position of the trunk marker switch, and front contacts of relays 135 and 113.

Relay 131 operates .relay 128, locks relay 135, releases .relay 136, opens the trunk marker switch restoring .path,provides a general holding ground for the trunk circuitand completes the dial impulse path Via back contact of relay 108, front contacts of relays 101 and 135, back contacts of relays 126 and 125, 'magnet 123 of the trunk marker switch to battery. The release of reiay 136 releases relay 112 which, in turn, reverses the polarity of the trunk conductors 116 and 111 to indicate to the operator that dialing may begin.

9 2,-Reception of the first, second and third digits It is assumed that the operator dials for line l' number 2341. At this time the register link and the register are attached to the trunk, the register link is prepared to operate on an incoming trunk call, and relay 128 of the trunk is operated.

' When the operator dials the first three digits of number 2341, relay 106 follows the dial pulses Y and repeats them to the register link by opening the loop to conductors 1|0 and 1| I via repeating coil 1|6, resistance 1| 1, and contacts of relays 128 and 106. When relay 108 rele-ases on each pulse, ground via the previously described impulse path operates magnet 123 of the trunk marker switch. The marker switch steps with the pulses and relay 1|4 operates in parallel with magnet 123 on the rst pulse and remains operated, due to its slow release characteristics, until the end of the pulses for each digit. Relay 1|5 operates from relay 1I4 and removes the ground from brush 120 of the trunk marker switch.

Relays 125 and 126 perform the function similarly performed in the register link circuit of determining whether 4the called line is within the same hundreds group as the trunk and whether the digit is dialed but distinguishes only between assigned and unassigned hundreds groups. When the trunk marker switch steps to a terminal corresponding toan assigned hundreds group, rel-ay 1|5 is released by the release of relay 1|4 at the end of the pulses. Relay 125 operates from ground, a front contact of relay 101, a back contact of relay 1|5, wiper 120 of the trunk marker switch, back contact and winding of relay 125 to battery. Relay 125 is connected i to terminals of wiper 120 corresponding to assigned hundreds numbers -and locks to relay 101, opens the dial impulse circuit, opens the path for operating relay 124 from the terminals corresponding to unassigned hundreds numbers and connects ground via wiper 120 to magnet 123 to y to position 11, ground via front contact of relay `101,'back contact of relay 1|5 and wiper 120 operates relay 124 to short circuit the impulse contacts of relay 108 and to reclose the impulse path f to magnet 123 and thus provide for receiving the impulses for the ringing digit on the trunk marker switch and preventing them from being received by the link marker switch. The pulses are received by the register link and register circuits to position the link marker switch in the register link, and the hundreds, tens, and units marker switches in the register.

If the trunk marker switch is stepped to a position corresponding to an unassigned hundreds group relay 126 operates via the Y connection to the bank terminals of wiper`120when relay 1|5 releases and the trunk circuit'is held in this condition until the register link releases.

3 Attachz'ng a trunk Zink A f-r'ee trunk link line finder is attached after the first digit is dialed. The operation of relay 335 connects battery via resistance 8|3, conductor 36|, the register link circuit .and link line nder brush 305 to conductor106. This applies test potential to the corresponding terminals of the line iinders vof the local links. Ground on conductor 629, line finder offnormal contact 628, back contact of relays 608 and 622, normally closed contacts of jack 62 0. winding of line finder clutch magnet 601 to battery operates the clutch magnet. All the local line nders, Whichare of lines capacity and similar to thelink line finders, that are idle, are started and hunt for the test potential applied to conductor 106 by brush 305 of the register link line finder. Conductor 106 is connected to the terminals over which the brushes 606 of the local line nders move.

When brush 606 encounters the test potential, relay 603 is operated in a circuit-from ground, back contact of relays S26-and 644, lefthand winding of relay 608,`con`tact of jackv 620, back contact of relay 622 tofbrush 606. Relay 608 operates and opens the clutch magnet 601 to stop the line finder. The start ground from conductor 629 is then connected through a front contact of relay 608, winding of relay 609, right hand winding of relay 698 to the test circuit. This forms the double test circuit and relay 606 will not hold when two or more are connected to the same test potential. One of them will release before the other and the one that releases rst stops the line iinder but does not connect through. The one that holds connects through and relay 62| operates and locks to ground on conductor 195 via brush 366 of the link line finder and the register link circuit. yThe starting circuit 'is deenergized, ground is disconnected from conductor 629 and test potential via resistance 8|3 is disconnected from conductor 36|.

The operation of relay 622 from a contact of relay 62| transfers line nder brush 606 from relays 608 and 609 to prepare for connecting to selector brush 6|5 Via contacts of relays 636 and 645. While relay 609 vis operated it closes a circuit frorn line nder brush 694 to operate relay 648 if group selection is required. Relay 648 locks to a ground at a contact of relay 622. Relays 608 and 609 release. The release of relay 609 prevents the locking ground for relay 648 from feeding back into the register link. Relay 622 opens the circuit to the line finder clutch magnet 601 to prevent the line nder from moving when test relay 608 releases and provides a holding ground for the link circuit.

4.-Selectz'on of o called Zine in same hundreds group Selection by the rst or hundreds digit is cancircuit is closed from ground in the register, conductor 31|,.wiper 323 of the register selector, through the register link circuit, brush 303 of l the link line nder, conductor 103, trunk line iinder brush 603, front contact of relay 62 back contacts of relays 631 and 636, selector oifnormal contact 630, winding of relay 6|8 to battery. Relay 6| 8 operates and extends the ground to clutch magnet 6|1 via conductor 8 6 to battery, to maintain the operation of the motor. The operation of the interrupter contacts 630 opens the starting circuit for relay 6|8 which locks to ground from the register. Selector oinormal contact 63| Y opens before oiTnormal contact 632 closes tozpre- Y 429. ground on brushl B| of the selector, as deter- 'f 136is released and conductor 103 is openin the trunk.

Ground pulses marking the beginning of each tens group are sent to the register via iinal selector brush 6| 6, back contacts of relays 633, 03S and 031, front contact of relay 02|, Ender brush 034, conductor 104, link line nder brush 304, through the register link circuit, register selector Wiper 324, conductor 312, to the winding of relay 429. Relay 429 operates the stepping magnet of the tens marker switch. The tens marker switch reaches position and fundamental ground is opened from wiper 323 of the register selector for' releasing' relayy EIB and v clutch magnet 5| 1 of the trunk link via conductor The register circuit is then prepared for selection. Therelease ofrelayl 0|3'and clutch magnet 511 stops the selector on the tens group as selected bythe tens marker switch. In this illustration,

the tens marker switch stepped from position 3` where it was set by the dial pulses, to position f Il Where it was driven by the revertive pulses from brush 0 6 of the selector.

The revertive impulse control circuit is now V closed over the previously described circuit from ground, conductor 31|, wiper 323 of the register selector, through the register link circuit, brush 303` of the link line iinder, conductor 103, brush |503y of the trunkline iinder, front contact of relay' 52|, back contactsv of relays 631 and 635, offnormalk contactv 630 to operate relay BIB. Clutch magnetV 0`|1 is' then operated to rotate the selector' brushes. When relay 6|8 operates, relay 534 operates via selector oifnormal contacts 032 and 63|. Relay 034V locks to ground from relay SiS,

prepares an operating-path for relay 033 and connects ground to the odd terminals of the group.

As the selector rotates the revertive ground pulses, in this example, from selector brush GIG, backv contacts of relays 633, B30 and G31, front contact of. relay 62|, trunk finder brush 604, conductor 104, brush 304 of the link line finder, through the register link circuit, Wiper 324 of the register selector, conductor 312, operate relay The iinal operation of relay 429 from mined by the positions of the tens and units marker switches in the register, removes ground fromconductor 31 `and relay 6| 8 and magnet 6 I 1 release, stopping the selector.v The register circuit now proceeds to test the called subscribers line.

5.--Test of called Zine When relay BIB in the trunk link releases, it

- opens the locking circuit for relay G34 and removes the short circuit on the Winding of relay 3-3which operates in series with relay 634 Which holds. Selector brush SI2 connects cutoff l relay 205 via conductor 225,`selector brush SI2,

front contact of relay 633, back contacts of relays E36 and 031, front contact of relay 62| trunk line finder brush |504, conductor 104, link line finder brush 304, through the register link, Wiper 324 of the register selector, conductor 312, winding of relay 422 to ground.

If the selected line is free, a test potential on selector brush 0|2 operates relay 422 and after If the selected line is busy, there will be no test 4potential on selector brush BIZ and relay 422 does not operate. When the slow relay operates, the line busy signal is sent to the register link.

lf2 When the register link. circuit receives a. line free or busy signal, one of two relays is operated to release the register and register link after signalling theA two-trunk circuit and the trunk link.

6.--Callcd line tests ,tree

The two-Way trunk controls the connection after the register link. is released, rings the called line or sends the busy signal to the operator and provides the transmission circuit for talking. Resistance ground in the register link. circuit is connected momentarily to conductor 31|, wiper 323 of the register selector, through. the register link, brush 302. of the link line finder, conductor 1.03, trunk line nder brush 623 operates relay EEB but not clutch magnet 0|?. The momentary operation of. relayl connects ground via va contact of relay 033 to short circuit relay 634 and hold` relay 633. Relay 635 operates Whilek relay 333 is held from aback contact of relay 634, locks to holding ground, connects trunk line finder brush E503 to' relays 04| and 642 and transfers the line test connection from contacts of relay 633 to contacts of relay 335 in preparation for the release of relay 633.

Upon receipt oi the line free signal the register link connects resistance 344 from battery, brush 325 of the link line i'lnder, conductor 10B and trunk line nder brush 306 to operate relay 542 Without operating relay 64|. Relay 642, in turn, operates relay 544 Which operates relay 6|9 via back contact of relay 626 and relay 631 and locks to holding ground from relay 622. Relay 5|9 connects the line circuit from conductors 100 and 19| vla trunk line finder brushes 600 and 5M and selector brushes SIB and 6H to line conductors 223 and 224. Relay 031 connects grounded resistance 039 via back contact of relay 043, front contact of relay B36, back contact of relay 641 andv selector brush 012 to conductor 224 to'hold the called line busy.

In the two-Way trunk the ground through high resistance 344, brush 305 of the link line nder and conductor also operates relay 133 which operates relay 142. Relay 14|] releases relay 128 and connects pickup ground on conductor 153, front contacts of relays 140, 124 and 123 to operate relay 133 which locks to a contact of ringing trip relay 132. Relay 133 releases relay 124 and connects the ringing leads via conductors and 10| and the trunk link to conductors 223 and 224 of the desired line and ring back tone to the trunk conductors 1|0 and 1|| via repeating coil HB. Ringing current is connected to conductor 10| or 102 by contacts of relay 149.

lt is noted that the operation of relay 133 is dependent upon the operation of relay 12B which is not operated until after the dial pulses of the ringing digit have set the trunk marker switch as will be described in section 8.

Relay 128, in releasing, transfers the connections to repeating coil H6 from the bridge resistance 1 1 to relay 121 to prepare for release super- Vision.

Ringing current is now sent to the called subscribers line conductors 223 and 224 from the harmonic ringing conductors 900 via brush 122 of the trunk rcarker switch, and Winding of the ringing trip relay 132.

'7.-Called Zine tests busy If the selected line tests busy, the register link circuit connects low resistance 340 from battery, link line nder brush 305, conductor 106, line nder brush 605 of the trunk link, to operate relays 64| and 642 in the trunk line. Relay 643 ,operates from relays 64I but relay 644, which is slow to operate, does not operate before relay 64| opens its operating path. Relay 643 holds from ground on line conductor 226 via selector brush 6i2 and connects ground to conductor 103 via a contact of relay 62| and trunk line nder brush 603.

Relays 131 and 138 also operate in the two-way trunk circuit from battery via resistance 340. Relay 138 closes the operating path for relay 140 from a back Contact of relay 131. Relay 140 does not operate before relay 131 operates and relay 139 operates from relay 131 on the busy signal. Relay 139 prepares the operating circuit yfor relay 14|. Ground from relay 643 of the trunk link via a contact of relay 62 I, trunk line iinder brush 603, conductor 103, a back contact of relay 136 and a front contact of relay 139 operates relay 13| which operates relay 129 in turn. Relay 109 operates in parallel with relay 139 and opens the transmission bridge to condenser 1|9. Relay 1I2 now operates from the y60 I. P. M. busy tone and ilashing ground interrupter connected to conductor 141, front contact of relay 129, back contact of relay 14|, front contact of relay 109 and back contact of relay 1I5 to reverse the polarity of trunk conductors 1|0 and 1I| to indicate to the operator that the desired line is busy. The operator may now release or monitor the line.

If the operator desires to monitor a busy line, she dials 1. This releases relay 108 momentarily and provides a ground pulse via back contacts of relays 108, 101, 135, 124 and 125 to operate relay 14| which locks to holding ground, releases relay 1I2, and connects the trunk to conductors 100 and 10| via condensers 15| and 152, thus permitting the operator`to monitor the call. When the line becomes free, relay 643 in the trunk link releases and removes ground from conductor 103 which releases relay 13| and, in turn, relay 129, which is slow to release. Relay 13| closes a momentary path for operating relay l140 to release relay 109, 139 and 14| in turn. Connection with the called line now proceeds as a call to a free line.

8.-Reception of fourth digit and ringing After the rst three digits have been dialed and recorded on the trunk, link, hundreds, tens `and units marker switches as described in section B-Z, the trunk marker switch has stepped to posiytion 1l and receives the pulses for the fourth digit to select the ringing current. Fully selective At this stage of the connection relays 124 and 126 are not operated. Relay 108 follows the dial pulses and repeats the pulses to the register link `to step the link marker switch. Magnet 123 is 'operated to step the trunk marker switch one step for each pulse 'in a circuit from ground, back contact of relay 108, front contacts of relays 101 and 135, back contacts of relays 126 and, 124, magnet 123 to battery. When the pulses cease, relay 1I5 connects ground via brush 120 of the trunk marker switch to operate relays 126 and 149 in accordance with the table. In this example, the fourth digit is 1 and the trunk marker switch tak-es one step toposition 12 and relay 126 is operated. As described in section B-6 when the line free signal is received from the register link and relay is operated, relay 133 operates if the trunk marker switch has been set by the dial pulses. If the dial pulses for the `ringing digit have not set the link marker switch, relay 133 awaits the operation of relay 126 to send ringing current to the selected subscribers line as described in section B-S.

The selection of a called line in a different hundreds group requires the selector of the trunk link to operate as a group selector to select a trunk to the selector of a free trunk link, serving the desired line. The terms group selector" and nal selector are used in the following 'description and the number designations for the final selector are primed When the trunk line finder is attached as described in section B-I, relay 648 is operated to transfer the trunk link conductors from group selector brushes 6I0 and 6|| to group selector brushes 6 |4- and 6 I5. Relay 641 operates from relay 648, disconnects group selector brush 652, connects group selector brush 655 to line nder brush 606 and connects group selector brush 6|5 to the link circuit for testing for a free trunk.

Selection is controlled by the register. Relay 622 has connected conductors 103 and 104 through trunk line nder brushes 603 and 604 to the trunk link circuit. Relay 6|3 is operated :from ground in the register circuit over conductor 103 and, in turn, operates the group selector clutch magnet 6I1. The group selector rotates to make the selection of the desired trunk group. The clutch magnet SI1 and relay 618 lock over oifnormal contact 630 to ground in the register' via conducto-r 103. Ground pulses marking the beginning oi the trunk groups are sent to the register via group selector brush 556, back contacts of relays 633, 633 and 631, front contact of relay 62 I, trunk finder-brush 504 and conductor 104. When the register receives that number of revertive pulses indicating the group selector is at the trunk group corresponding to the digit dialed, it removes ground from conductor 103 to .stop the group selector and releases relay 6 6 and of selection relay 636. As the group selector rotates, the register is testing the trunks for a free or busy condition Via conductor 106, trunk line finder brush 606, front contact of relay 622,

yback contacts of relay 33,6'and 345, front contact of relay 541 and group selector brush 6%5. Relay 63,4 remains operated and relay 333 operates in series with it. Relay 636 now operates over front connects resistance ground, momentarily, on vconmessage ductor 183'. to operate. relay 5.1.3 which,` inturn, operates and shunts thev winding of relay 634 which releases. Relay 833 locks; to relay G18 but releases after relay B18 releases.` when the ground. is removed'. by the register.. Relay 63E, whichv operated with relay 633, locksto ground on relay E22 and connects selector. group. brush 6151trelayf635.

Ground through the winding'of relay 53.5, group selector brush 51.5" and conductor B25 operates relay E26 oythe free final selector. Relay S26 operates relay 522 which connects conductors i523 andv B2i to the nal selector circuit in place cf` the connections from line finder brushes S33' and Std' of the selected trunk link in which the associated selectorf now operates asv a nal selector.

fall the trunksto thev nnal selector are busy the register sends a busy signal to the register link. Ground is removed from conductor 3'51 by the register to release relay 61% and clutch inagnet 6H and stop the rotation of the group selector. The line busy signal is sent from the register to the register link and battery through resistance 349 of the register link circuit, is connected to brush 365 of the link line finder, conductor 105, front contact of relay '135, windings Yof relays '131 and 138 in the trunk circuit and ground. The resistance 3M is of such Value that relays 13'! and '138 both operate. Relay 'Mil is prevented from operating, because of its slow operating characteristic, and relays 'i3d and 'lil operate from ground at a front contact oi relay '131. The operation of relay ille connects the 120 I. P. M. flashingV interrupter via conductor 14S, back contacts of relay 129 and lill, a iront contact of relay '109, a back contact of relay 115, winding of relay 'H2 to battery. Relay 'H2 reverses the current to trunk conductors lli) and 'H1 at a rate of 120 reversals per minute to signal the operator that the trunks are busy and that the connection should be immediately released by opening the trunk conductors and releasing relay 108.

Whenever a flashing signal from the interrupters 60 or 120 I. P. M. over conductors 'M6 and 74, depending upon the released or operated condition or relay T29, is used as a flashing signal through the operation of relay l' i2, as previously described, over trunk conductors 'il S and 'il 1, an interruptor busy tone at the same rate over conductors 144 and 145, similarly depending upon the released or operatedv condition of relay 72S, is connected through a back Contact of relay 141, condenser E52, a front contact of relay '39 to the repeating coil 'E16 to give the operator an audible signal thatV either all the trunks are busy or that the called line is busy.

The selection of the desired line is made as described in section B-4 the fundamental circuit being connected to the register via conductor 623 and 524, brushes 513 and 61d, back contacts of relay B45, front contacts o relay '6138 and front lcontacts of relays S19, E3? and 21 of the foreceding group selector, associated trunk line :finder brushes S and Elie and conductors '593 and Tile.

The test of the selected line is made by the register and the iinalselector as described in section B-5. The free line signal is passed through the group selector when relay $42 operates and, in turn, operates relay 644. The operation of relayllf. connects battery via resistance 613s, a back-contact of relay 61s, resistance 542, y.iront contact of relay 64d, back contact of relay ...645,group selector brush 6.43, 'conductor $23 to windings. ofn relays 41 and' M2' or the; final selector' to ground. Relay 642 operates as described in section. B-5. Relay ESIS is operated in the group selector to transfer the group selec.- tor brushes 613 and 61d from nder brushes 693 and 6&4k to finder brushes '59S and 89|. The register link releases but relays S21 and 522 are held operated by the two-way trunk via iinder brush 635, conductor T65, back contact of relay Z135, front contacts of; relays 'Mtl and 19.1 to ground.

When a busy signal isV received'from. the register link relays 54! and 642 both operate. Relay 544( repeats the low resistance battery byv connecting resistance Edil via group selector brush S13 and conductor i523 to relays 64I and 652' of the nal selector. Relay tilt operates4 and connects ground via a contact or relay B21, trunk line finder brush 663 and conductor 'm3 to operate relay '131 of the two-way trunk circuit as described in section B-E. Relay 619 operates to connect the line wires throughV the group. selector to the nal selector and the circuit awaits the freeing of the busy line or releasev by the two-way trunk circuit.

1er-Talking, supervision and release At the end of section B-E it is noted that ringing current is connected to the line conductors through a winding of the ringing trip relay '132 when relay 733 is operated. When the called subscriber answers the ringing trip relay '132 is operated and relay 133- releases. rihe called subscribers line connected through the trunk link to conductors lill) and '10i is extended through back contacts of relays 'F33 and 139 to the repeating coil 'F18 and talking battery is supplied through the windings of relay 121 which operates. Relay '121 operates relay 'H2 to reverse the current to trunk conductors 'Mil and 11E to signal the operator that the call has been answered. Supervision to the operator is obtained by the release and operation of relay 'i12 under control of relay '52? which, in turn, is controlled by the called subscriber. If the operator should wish to recall a subscriber who has hung up she will dial l which releases relay 7&8 and connects ground via back contact of relay 103, front contacts of relays lill, '135, 126 and E25, back contacts of relays 'Ml and 139 to operate relay 12e. The pickup interrupter is now connected over conductor '.153 through front contacts of relaysy Nil, 'E24 and 72S to operate relay 123. Ringing is now applied to the calling subscrihers line as previously described.

When the subscriber disconnects nrst, relay 12'1' releases and, in turn, releases relay '1 l 2 which reverses vthe polarity of trunk conductors 'H0 and 'H1 indicating to the operator that the call is completed. The trunk waits for the disconnect by the operator which will release relay lllland, in turn, relay 713 and lll?. Relay lb?. removes holding ground from conductor 'lll-5 and the remaining relays which now release and. free the trunk circuit. The trunk marker switch returns to normal via its own interruptor contact, brush 'l2l and a contact of relay TS1. When holding ground is removed'from conductor 'm5, relays 521 and 622 release. Relay 622 removes the holding ground for the trunk Ylink'circuit which releases. The group selector returns to its normal position, clutch magnet 617v being energized from 'ground onoffnormal contact B32 via back contacts of relays4 eand 622. The .final selector is releasedv from the group selector by removing 17 the grounded winding of relay 635 from conductor y625 to release relay 626' of the nal selector circuit. The release of relay 626 releases relay 622 which opens holding ground and closes the circuit for'restoring the final selector to normal.

When the operator disconnects, first relay 108 releases and releases relays 'H3 and 'E01 which, in turn, removes holding ground for the remaining relays with the exception of relay 121 and 112. Relay 121 releases when the trunk link opens the circuit to the subscribers line vand releases relay 'l I 2. The release of relay 205 of the line circuit connects the line and lockout relays, not shown, to the line to hold the line circuit in the lockout condition until the subscriber hangs up.

While we4 have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description isv made only by Way of example and not as a limitation to the scope of our invention.

What is claimed is:

1. In an automatic telephone system a central oiice, a community office including subscribers lines divided into groups, each group designated by the first digit of the line number, groups of register links corresponding to said groups of lines, each link comprising a line finder having certain of its contacts connected to the lines of the corresponding group and a register selector, registers connected to the contacts of said register selectors for controlling the selection of a called line, a two-way trunk circuit in the community oiiice including a rotary switch for completing the connections between the subscribers lines and the central ofce, calling dials at the central oiiice for controlling the sending of digit pulses representing numbers, means in the two- Way trunk circuit responsive to dial pulses from the central oice for operating the rotary switch of the trunk circuit and for repeating the dial pulses to a selected one of said registers, means in the trunk circuit controlled by the rotary switch for distinguishing between rst digit numbers representing assigned and unassigned groups of lines, land further means in said trunk circuit responsive to the position of the rotary switch for holding said trunk circuit when' 'said rotary switch is in a position representing an unassigned group of lines.

2. The system according to claim l, and, in addition, means for releasing the register link responsive to the pulses of the first digit dialed :for an unassigned group of lines and means conftrolled by said releasing means for releasing said 'trunk circuit.

S. In an automatic telephone system, a central 4office, a community ofce including a subscribers lineair incoming trunk circuit in the community omce connected to the central cnice, a calling dial for sending digit pulses at the central oiiice connected to said trunk circuit for selecting the subscribers line over said trunk circuit, a register link comprising a line finder having contacts connected to said trunk circuit and a register selector, a register for controlling the establishment of a connection between the central oince and `said subscriber line, said register being con- 18 circuit responsive vto the pulses of the first digit dialed by said calling dial, and means in said trunk circuit determined by the position of said rotary switch in accordance with the rst digit vdialed to distinguish between an assigned and an unassigned line group.

4. In an automatic telephone system, a two- Way trunk circuit including a rotary switch connected to a central oce, a subscribers line having a three digit call number, a register, a register link comprising a line finder having contacts connected to said two-way trunk circuit and a register selector having contacts connected to said register for connecting said two-way trunk circuit to said register, a calling dial connected to said trunk circuit at the central oflice for controlling the sending of digit pulses representing numbers, means in said trunk circuit for operating said rotary switch under control of the dial pulses and for repeating the pulses to said register link and 'to said register, said means including means for stepping said rotary switch one step for each impulse of the irst digit, means -for thereafter stepping said switch to a predetermined position, and means for thereafter stepping said switch one step each for the second and third digits and means for utilizing subsequent movement of said switch for transmitting ringing current to said subscribers line.

5. In an automatic telephone system, a multiparty subscribers line, an incoming trunk circuit including a rotary step-by-step switch, a calling dial connected to the distant end of said incoming trunk circuit for controllingthe sending of digit pulses representing numbers, a register for establishing connections from said incoming trunk circuit to a party on said subscribers line, a register link including a line finder having contacts connected to said incoming trunk circuit and a register selector having contacts connected to said register for connecting said register to said incoming trunk circuit,` a trunk link including a line finder having contacts connected to said incoming trunk circuit and a selector having contacts connected to said subscribers line for connecting to said subscribers line, switch means in said incoming trunkcircuit, means controlled by said switch means for causing said register link to connect said register to said incoming trunk circuit, means including said rotary switch for operating said switch means in accordance with the pulses of a predetermined number of digits and for repeating said pulses to the register link and said register, means in said incoming trunk circuit for blocking the transmission of pulses of succeeding digits of the call number to said register link and said register, and means controlled by said last-mentioned means for operating said rotary switch in accordance Withthe pulses of succeeding digits.

6. In an automatic telephone system, a multiparty subscribers line having a four digit line number, the first three digits of the line number `designating the line terminal and the fourth digit designating a party on the multi-party line, an incoming trunk circuit includinga rotary stepby-step switch, a calling dial connected to the distant end of said'trunk 'circuit for controlling the sending of digit pulses representing numbers, a register for establishing connections from said incomingv trunk circuit to said subscribers line, ya register link 'including a line finder' having contacts connected to said incoming trunk circuit vand a register selector having contacts cony nected to said register for-connecting said regisiter tto; said :trunkgcircuitna trunk. lnkincluding .a line.' iinder :having contacts connected to sai-d .incoming trunk circuit andV aselector'havingcontacts connected to saidlineffor-.connecting `said L.trunk .circuit to said subscribersline, .means .in said incoming trunk `circuit .for :stepping said vrotary switch' one; step for .eachpulse .of the rst digit received. from. said callingdial .and one step each for the next two digits, means controlled by said rotary. switch fonrepeatingthepulses .of the. iirstpthree .'dststo said: register link and said register, means icontrolledrby; said. register in, response to the;pulsesfreceived'zthereby for operating the selectorinsaidftrunk link to connectsaid trunk circuit with said line, means in said incoming trunk circuit forffurtherstepping they rotary switch in laccordance with .the Ypulses of the fourth digit receiredfrom-said.callingfdial, means controlled by said rotary switch. for blocking ythe repetition of the pulses of the fourth `digit 'to said register link and-.saidzregisterfand Vmeans in said incoming trunk :circuit depending upon the -position of the rotary switchior applyngxringing current to signaliaidesired called -partyon said subscribers line.

7. In an automatictelephone system,1av multiparty subscribersline, anzincomingitrunk .cir-

cuit including a yrotary tstep-by-step '.switch, a register for establishing Vconnections from said incomingtrunk circuit .to said subscribers line, iaY register link Jincludinga fline nderih-aving .contacts-,connected .to-.said incoming trunk circuit and a'register'.selectonhavingcontactsconnected to said #register fior :connecting said register to -said incoming-trunk'circuit, a-trunk iin-k includ- Ying a line -nder vhaving ,contacts connected to said incomin-gitrunk circuit andsJ selector having lcontacts vconnected -to -said line for connecting said incoming 'trunk .circuit to saidv subscribers line, means in'said incoming trunk circuit for operating said Vvregister link line nfinderto -con -nect said registertofsaidincoming trunk'circuit, meansin said incoming Atrunk Acircuit responsive toA the dialling .ofwa'predetermned number of -digits for setting said registerin accordance therewith, meansacontrolled by the setting -of said registerfor operating .the trunk. linkse- .lector toconnectzsaid trunk circuit to .saidjsubscribers.- line, g and. means in r,said `trunkv circuit responsive to "the dialling .of .--a digit 1suffix vfor :selectively xoperatingssaid. rotary4 switch .to :apply ringing current to zsignal :adesired .called party on said subscribers line.

8. In fanautomaticl telephone system, fa illurality of subscribers lines, nanncoming trunk, registers for establishing :connections from@said incoming trunk1tora1called1one ofsaid subscribers lines, registerglinks including line v'finders lhaving cont-acts connected itofsaidA incoming :trunk and register-selectors having contactsrconnected to said registers forV connecting one of'said. registers :to said incoming trunk,trun1 linksjincluding line finders having 'contacts :connected to .said incoming :.trunk-A andiselectors'- having: .contacts 'connected' to said lines for-connecting said' incoming trunk toa oalledfoneot.saidfsubscribers lines,

:means in-saidregistersfresponsive .tothe completion of'connectionstoa called/one of saidnsubscribers lines dorf-determining the busy or idle condition ofsaid line,1and. means in said incom- -`'ing trunk responsive 'to said vlast mentioned means in; said yregisterrtoftransmita busysignal VVscribe1"s..line; .an incoming trunkl :a calling `dial '20 -connected tothe :distanteend :of said. incoming trunk .for controlne .the sending of :digit pulses .representing` numbersraregister for establishing connections from :said ,incoming :trunk to said subscribers line, aA register-.link including a line finder having contacts connected to said incoming trunk and@register-selector having contacts connected-t0 saidregister Yfor connecting said register to. said incoming trunk, a trunk link including aline finder having contacts connected to :said -incomingt-runkand Aa selector having contacts connected V.tosaid vline for connecting said .incoming trunkftorsaid Asubscribers iine, means in saidincoming 4trunlsfor transmitting a, ashingbusyfsignal to therdistant end of said incoming trunk, means' inisaid `register responsive to the completion of a connection to a called :line for testing-thebusy or idle condition of said .called line andior.1transmitting aline free or line busy signal to .said ,incoming trunk, and means in said incoming .trunkresponsve to the receipt of a, line busy sgnalorgtransmitting the fiashing busy signal to the distantend of said incoming trunk.

10. The systemaccording to claim 9, and .in which said incoming trunk includes a rotary .switch.respo.nsive to the..digit .pulses from the -callingdial wherbyitrsselectively operated for applying ringing current .toacalled subscribers line, .andmeansin saidincoming trunk upon receiptofa line free signal iOrappiying. ringing currentinaccordance .with saidposition of the .rotaryswtch tosaidcalledsubscrbers. line.

,1.1. v.The system., according ...to claim 9, and .in whichsaidsuhscribers lineis.. arnulti-party line.

12.'.The-system according .to claim .9, and in which said subscribersline,.register links, and

.-said trunk .links arejdividediinto groups according tothe first `digito"f..thecalled number, the .trunklink selectonhavinglcertain other of its .contacts connected to other trunk links and Aivhena call is madefora line ingv group to which said incoming trunk' is notconnected, the selector ofthe associated trunk link operates asa group selector to .select a trunk link .of the desired group andoperates the selector thereof as a final selector allunder the control of said register, and .meansjinsaidincoming,trunk responsive to the receiptcf the busy'signal indicating that all the :incoming trunks ,to the Y'iinal.selectors are busy,

for transmitting aiiashing'signal to the distant end of said incoming trunk.

,13. The system according to claim 9, and in which the Vmeans .1in said lincoming trunk for receiving the linefiree or line busy signal comm prises .two relays, VKone of :which is operated to "transmit a busy signal, and the other of which .is .operated to indicate line free.

*HOWARD.G. DUHAMEL.

.EDY/YARD O. CAMPBELL. RAYMOND A. REED.

"The following references fare of record in the 'file of Ytlriis-pa-tent:

.UNI'I'EDLSTATES PATENTS Number Name vDate 1,450,321 .:Lundel1 Apr. 3, 1923 1,482,618 '-Polinkowsky Feb. 5, 1924 .1,575,140 .Willams Mar. 2, 1926 "2,108,140 `laiiterson Feb. l5, 1933 ,2,250,101 L,IIubbard. July22, 194i vv2,339,709 Os'tline Jan. 18, 1941.1. 2,447,494 Deakin Aug. 2.4, 1948 

